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Showing papers on "Nanocomposite published in 1993"


Journal ArticleDOI
TL;DR: The sol-gel process, with its associated mild conditions, offers a new approach to the synthesis of composite materials with domain sizes approaching the molecular level as mentioned in this paper, where transparent organic-inorganic composites can be prepared by dissolving preformed polymers into solgel precursor solutions and then allowing the tetraalkyi orthosilicates to hydrolyze and condense to form glassy SiO, phases of different morphological structures.
Abstract: The sol-gel process, with its associated mild conditions, offers a new approach to the synthesis of composite materials with domain sizes approaching the molecular level. Transparent organic-inorganic composites can be prepared by dissolving preformed polymers into sol-gel precursor solutions, and then allowing the tetraalkyi orthosilicates to hydrolyze and condense to form glassy SiO, phases of different morphological structures. Alternatively, both the organic and inorganic phases can be simultaneously formed through the synchronous polymerization of the organic monomer and the sol-gel precursors. Depending upon such factors as the structures of the organic and inorganic components, the phase morphology, the degree of interpenetration, and the presence of covalent bonds between the phases, the properties of these composites can vary greatly and range from elastomeric rubbers to high-modulus materials.

1,347 citations



Patent
08 Apr 1993
TL;DR: In this paper, a method of fabricating three-dimensional objects in a layerwise fashion, and having high structural strength and high density, is disclosed, where a laser fuses selected portions of layers of the powders according to a computer-aided-design data base.
Abstract: A method of fabricating three-dimensional objects in a layerwise fashion, and having high structural strength and high density, is disclosed. Methods are disclosed by which nanocomposite powders of ceramic-ceramic systems, ceramic-metal systems, ceramic-polymer systems, and metal-polymer systems are produced. Disclosed examples utilize solution chemistry approaches, such as sol-gel processing, by way of which a gel is produced which is then fired and milled to form a powder suitable for selective laser sintering, where a laser fuses selected portions of layers of the powders according to a computer-aided-design data base. The ultraheterogeneity of the powder results in larger surface area and grain boundaries of the constituents, which enhances the solid state diffusion mechanism, and thus reduces the time and temperature required for sintering to occur. In addition, the higher stored metastable energy of the nanocomposite powder is believed to enhance densification during solid-phase sintering. Objects of high density of complex shape may thus be obtained directly from CAD data base design representations.

150 citations


Journal ArticleDOI
TL;DR: In this article, a spincoating process was used for the preparation of nanocomposite films with controlled thickness, e.g., between 40 nm and 2 μm for a film containing 45 wt.% PbS.
Abstract: Solutions of PbS particles and gelatin were used for the preparation of nanocomposites by a spin-coating process. This allows for the preparation of nanocomposite films with controlled thickness, e.g., between 40 nm and 2 μm for a film containing 45 wt.% PbS. Surface roughness and film thickness were investigated by surface profilometry and scanning electron microscopy (SEM). The refractive index at 632.8 nm can be expressed by a linear function of the volume fraction of PbS in the range of 0 to 55 vol. % PbS. In this range, the refractive index increases from 1.5 to 2.5 with increasing PbS ratio and belongs, therefore, to the highest refractive indices known for polymeric composite materials.

115 citations


Journal ArticleDOI
TL;DR: In this paper, a polypyrrole-silica colloidal composites by chemically polymerizing pyrrole using either FeCl 3 or (NH 4 ) 2 S 2 O 8 oxidants in the presence of small colloidal silica particles is presented.

85 citations


Journal ArticleDOI
TL;DR: In this paper, the role of intermediate phases in understanding the mechanism of mechanochemical processes is emphasized, and the reduction of Cr 2 O 3 by aluminum or zinc and reduction of Fe 3 O 4 by zinc are identified as promising candidates for further investigations.

59 citations


Journal ArticleDOI
TL;DR: In this article, the Mossbauer spectra of Fe/SiO2 samples are comprised of a ferromagnetic component superposed on a superparamagnetic doublet, and the materials show enhanced coercivities.
Abstract: Glass‐metal nanocomposite powders in the systems Fe/SiO2 and Ni/SiO2 have been prepared by the sol‐gel technique followed by reduction treatment. Bulk nanocomposites are then fabricated by hot pressing these powders. The metal particle diameters range from 8.9 to 14.8 nm. The materials show enhanced coercivities, e.g., a maximum of 82 Oe in the case of Ni/SiO2 and a maximum of 474 Oe in the case of Fe/SiO2 systems. The Mossbauer spectra of Fe/SiO2 samples are comprised of a ferromagnetic component superposed on a superparamagnetic doublet.

47 citations


Journal ArticleDOI
TL;DR: In this paper, a procedure for obtaining nanocomposite powders consisting of metal nanoparticles homogeneously dispersed within alumina grains is described, where the larger particles are nucleated in Fe2O3 overconcentration zones.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that high surface area and mesoporosity can be preserved in the above nano-composite aerogels by heating at 1000 °C.
Abstract: Monolithic nanocomposite aerogels of two aluminosilicate compositions have been prepared and characterized by different techniques. The results show that high surface area and mesoporosity can be preserved in the above nanocomposite aerogels by heating at 1000 °C, unlike the single component aerogels. The presence of alumina as a second phase prevented their densification which resulted in surface areas on the order of 500–600 m2/g and mesopores of about 5–6 nm in diameter after heat treatment at 1000 °C. These novel nanocomposite aerogels are expected to find applications at high-temperatures in separations, insulation, catalysis, etc.

42 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic properties of both mechanically alloyed Fe-Cu and the nanocomposite phase produced at intermediate ball milling times were studied and shown to have magnetic properties similar to those of Fe-cu films prepared by vapor-quenching.

38 citations


Patent
28 Jan 1993
TL;DR: In this paper, an element formed of such a nanocomposite superparamagnetic material is reciprocated into and out of a heat exchanger within a controlled magnetic field and is in heat transfer communication with a second heat exchange to facilitate the production of a refrigeration heat transfer effect thereby.
Abstract: A nanocomposite superparamagnetic material that includes nanosize particles of a magnetic component, preferably a rare earth and a transition element, dispersed finely within a bulk matrix component provides finely dispersed magnetic clusters, whereby a high magnetocaloric effect is obtained in using the nanocomposite material in a conventional magnetic refrigeration system. In one aspect of the present invention, an element formed of such a nanocomposite superparamagnetic material is reciprocated into and out of a heat exchanger within a controlled magnetic field and is in heat transfer communication with a second heat exchanger to facilitate the production of a refrigeration heat transfer effect thereby. In another aspect of the present invention, a generally disk-like element formed of the nanocomposite superparamagnetic material is rotated so that portions thereof move between a first heat exchanger and a second heat exchanger that is within a controlled magnetic field, to thereby perform refrigeration heat transfer between the two heat exchangers.

Patent
09 Nov 1993
TL;DR: In this article, a composite formed from a gamma phase polyamide such as nylon (6) having dispersed therein a particulate material such as a phyllosilicate as for example montmorillonite is described.
Abstract: This invention is directed to a composite formed from a gamma phase polyamide such as nylon (6) having dispersed therein a particulate material such as a phyllosilicate as for example montmorillonite

Journal ArticleDOI
TL;DR: In this article, the authors showed that the mean magnetic moment of iron in these nanocrystals is larger than that in bulk metallic iron, and the interfacial phase surrounding some iron particles was identified as an antiferromagnetic phase, Fe1+xAl2−xO4.
Abstract: Iron-alumina nanocomposite powders containing 10 wt % iron were prepared by selective reduction of alumina-haematite solid solutions Microstructural study showed three types of metal dispersion in the alumina matrix according to the elaboration process: iron grains that were >70 nm, most of the iron particles were <10 nm and directly epitaxied in the alumina matrix, and iron particles that were surrounded by an interfacial phase In agreement with transmission electron miscroscopy (TEM) observations, magnetic study confirmed a distribution of the iron particles size, showing the superposition of a ferromagnetic behaviour (larger particles) and a superantiferromagnetic behaviour (smaller particles) Furthermore, analysis of thermoremanent behaviour, coercive field and dissymmetry of hysteresis loops allowed the interfacial phase surrounding some iron particles to be identified as an antiferromagnetic phase, Fe1+xAl2−xO4 Nevertheless, at the interface of metallic iron epitaxied on the alumina matrix some atomic planes always existed where iron was ionic (even if no other phase was detected) As a consequence the mean magnetic moment of iron in these nanocrystals is larger than that in bulk metallic iron

Journal ArticleDOI
TL;DR: In this article, electrical conduction was studied as a function of film thickness, film deposition rate, composition, time, and temperature, and the electrical conductivity in pure CaF2 adjacent to an Al2O3 interface sometimes exceeded the bulk CaF 2 conductivity by as much as a factor of 6700 at 200°C.
Abstract: Thin films of pure CaF2 and nanocomposite mixtures of Al2O3 with CaF2 were evaporated on Al2O3 substrates. Interdigital electrodes on some of the substrates allowed in situ measurements of the electrical conduction in the films during and subsequent to film growth. Electrical conduction was studied as a function of film thickness, film deposition rate, composition, time, and temperature. The electrical conductivity in pure CaF2 adjacent to an Al2O3 interface sometimes exceeded the bulk CaF2 conductivity (i.e., value at more than 50 nm distance) by as much as a factor of 6700 at 200 °C. The high conductivity is characterized by an activation energy of 0.6±0.1 eV, which is significantly lower than the activation energy of about 1.0 eV for conduction in the bulk. However, this high conductivity is thermally unstable and diminishes in time. A high but stable conductivity was obtained in CaF2 films containing about 10 mol % Al2O3 as a dispersed second phase. At 200 °C, a two‐phase film gave a factor of 360 enh...

Patent
04 Feb 1993
TL;DR: In this paper, a ceramic nanocomposite comprising a porous ceramic coating having a silicone polymer within the pores was described as a protective coating on an electronic device, which is a preferred embodiment of the invention.
Abstract: The present invention relates to a ceramic nanocomposite comprising a porous ceramic coating having a silicone polymer within the pores. In a preferred embodiment of the invention, the ceramic coating is a protective coating on an electronic device.

Journal ArticleDOI
M.B. Bush1
TL;DR: In this paper, a computer model has been developed which treats separately the crystalline and grain boundary regions for nanophase palladium and has been used to determine the effective elastic properties of the grain boundary region for that material.
Abstract: Nanophase or nanocrystalline materials are polycrystals in which the grain size ranges typically from a few nanometers to a few tens of nanometers. Under these conditions the volume occupied by the grain boundary region may represent 50% or more of the total material volume. The unique properties of the grain boundary then have a significant influence on the bulk behaviour of the material. A computer model has been developed which treats separately the crystalline and grain boundary regions. By utilizing measured data for nanophase palladium, the model has been used to determine the effective elastic properties of the grain boundary region for that material. The model demonstrates that the Young's modulus varies with grain size in a nonlinear fashion that is not adequately represented by existing theoretical models. With the aid of a model of this type, it is then a relatively simple matter to investigate features such as sensitivity to changes in the grain aspect ratio and the result of adding further phases to form more complex nanocomposite materials.

Journal ArticleDOI
TL;DR: In this paper, the thermal stability in air of these materials was studied by differential thermal and analysis X-ray diffraction. Magnetic parameters such as coercitive field, magnetization, etc. were also measured.
Abstract: Optically clear monolithic (OCM) gels of alumina and aluminosilicates can be prepared by hydrolysis-polycondensation of alkoxides. Subsequent heating induces transformation firstly into OCM mesoporous glasses and then into dense translucent or optically clear ceramics, the densification occurring at low temperature. Immersion of alumina or aluminosilicate gels and glasses in aqueous solutions containing transition metal (cobalt, iron, nickel) ions leads to diffusion of these ions into the water within the pores of the monoliths. After heat treatment under hydrogen, metallic nanoprecipitates are obtained. The size of the precipitates, as studied by transmission electron microscopy, ranges from 5 to 70 nm depending on the host matrix. The thermal stability in air of these materials was studied by differential thermal and analysis X-ray diffraction. The oxidation of porous composites occurs above 600 °C in air. Magnetic parameters such as coercitive field, magnetization, etc. were also measured.

Journal ArticleDOI
TL;DR: In this article, a thermochemical conversion of a Fe-N/BN-containing precomposite synthesized via an aqueous chemical route is described, and structural, chemical, morphological, and magnetic properties are presented.

Journal ArticleDOI
TL;DR: In this article, the authors used diverse matrices, such as an ion exchange resin or a porous glass, to prepare stable nanocomposites of several materials including iron oxide and lead iodide.

Journal ArticleDOI
TL;DR: In this article, the relative amounts of TiC and SiC as well as the microstructure depend on the SiH[sub 2]Cl[sub 4] content in the initial gas-phase mixture and variations of composition of the of the deposits are in good accordance with the thermodynamic calculations.
Abstract: Microcomposite and nanocomposite structures composed of SiC-TiC and C have been prepared by chemical vapor deposition at atmospheric pressure (APCVD) from an initial gaseous mixture with the composition C[sub 4]H[sub 10]-SiH[sub 2]Cl[sub 2]-TiCl[sub 4]-H[sub 2]. Transmission electron microscopy reveals that deposits with a nanocomposite structure consist of a network of 10-nm-thick needles surrounded by small areas of amorphous carbon. The relative amounts of TiC and SiC as well as the microstructure depend on the SiH[sub 2]Cl[sub 2] and TiCl[sub 4] content in the initial gas-phase mixture. The variations of composition of the of the deposits are in good accordance with the thermodynamic calculations. Amorphous carbon is always present in the deposits. This amount can be lowered to 1 at. % at low deposition temperatures but, at such a concentration, still has a great influence on microhardness. The variation of the preferred orientation of crystals is also discussed with respect to the composition of the samples and the deposition temperature.

Journal ArticleDOI
TL;DR: In this article, the microstructures and properties of the C/C-SiC nanomatrix composite prepared by codeposition were described, and the experimental set-up is illustrated in Fig. 1.
Abstract: C/C composites are widely used as structural materials at high temperature in the aeronautic and space industries [1, 2]. A serious drawback, however, is that carbon in any form will react with oxygen, burning away rapidly at temperatures as low as 500 °C. Since the C/C composites are generally made of several types of carbon, each having its own reactivity to oxygen, the reactivity of carbon matrix would influence the oxidation performance of the C/C composites. In order to improve the oxidation resistance, carbon matrix has been partially or even totally replaced by other refractory materials which can be carbide or nitride. This family of materials were defined as hybrid carbon-ceramic composites, which can be made according to a two-step chemical vapour infiltration (CVI) procedure [3]. One material receiving considerable attention recently is the "functionally graded material" in which the material properties are continuously changed by gradually varying the dispersion-to-matrix ratio from one surface of the material to the other surface. Among these "functionally graded materials", one that consisting of silicon carbide (SIC) and carbon (C) was prepared by the chemical vapour deposition (CVD) technique through a codeposition process using multicomponent gas reactions. This material is called a nanocomposite because of the SiC of nm size dispersed in the pyrocarbon coating. An improvement in the oxidation resistance has been reported when a small amount of SiC (< 5 tool %) is combined with the carbon matrix by CVD [4]. CVD SiC-C containing a trace of carbon was shown to be more resistant to abrasion than CVD SiC. The aim of this study was to prepare carbon fibre-reinforced C-SiC nanomatrix composites, but not nanocomposites, by the CVI technique through the codeposition process. This letter describes the microstructures and properties of the C/C-SiC nanomatrix composite prepared by codeposition. The experimental set-up is illustrated in Fig. 1. CH3SiC13 liquid and C2H2 gas were used as the source, and H2 and N2 gases were used as the carrier and dilutant gases, respectively. The deposition temperature was selected as l l00°C, the total pressure 1000 Pa and CH3SiC13 was carried into the furnace by bubbling H2 carrier gas. The CH3SiC13 vapour flow rate was controlled by the H2 carrier gas flow rate. The gas flow rates were N2 0.1 m 3 h -1 , H 2 0.0018-0.0024 m 3 h -1 and C2H2 0.02 m 3 h -1. The carbon fibre preform was polyacrylonitrile-based carbon felt of density about 0.1 g cm -3. After

DOI
01 Jan 1993
TL;DR: The sol-gel process allows the synthesis of inroganic non-metallic materials through a soft chemistry route and organic functions can be incorporated as discussed by the authors, allowing the inorganic part to be linked chemically to the organic one.
Abstract: The sol-gel process allows the synthesis of inroganic non-metallic materials through a soft chemistry route and organic functions can be incorporated. While maintaining the phase size of the inorganic component on a molecular or nano range, inorganic molecular or nano composites can be fabricated. For this reason techniques that make use of surface interaction controlling ligands for colloidal sol-gel particles have been developed, allowing the inorganic part to be linked chemically to the organic one. Using these principles, new nanocomposites for optical application and for coatings with special properties (anti soiling, corrosion inhibition) have been developed.

Journal ArticleDOI
TL;DR: A comparative study of laser-produced nanocomposite ternary Si-C-N powders, obtained from different SiH 4, amines and NH 3 mixtures, is presented in this paper.
Abstract: A comparative study of laser-produced nanocomposite ternary Si-C-N powders, obtained from different SiH 4 , amines and NH 3 mixtures, is presented. It is shown that the final composition of powders is correlated with and may be controlled by the experimental parameters. Preliminary results on laser irradiation of SiH 4 , NH 3 and (CH 3 ) 3 Al mixtures demonstrate the possibility of producing nanosized powders composed of a matrix of Si 3 N 4 with a different content of Al

Journal ArticleDOI
TL;DR: Amorphous Si-Zr-N-O powders, obtained by nitridation in an NH3 flow of zirconium modified polycarbosilane, have been sintered to full density by hot pressing at 1500‡C as mentioned in this paper.
Abstract: Amorphous Si-Zr-N-O powders, obtained by nitridation in an NH3 flow of zirconium modified polycarbosilane, have been sintered to full density by hot pressing at 1500‡C. The resulting ceramic shows an extremely fine-grained microstructure composed of Si2N2O and ZrO2 crystallites 20–30 nm in diameter. Thermal stability measured in air appears excellent up to 1300‡C for 48 h. Mechanical characterization pointed out good values of flexural strength (330 MPa), fracture toughness (4.1 MPam0.5) and Weibull modulus.

01 Jan 1993
TL;DR: In this paper, a new materials design was established for the structural ceramics to break through the present monolithic and composite materials, where the ceramic-based composites were divided into two groups: micro and nan composites.
Abstract: The new materials design was established for the structural ceramics to break through the present monolithic and composite ceramics. In this concept, the ceramic-based composites were divided into two groups: micro and nanocomposite. The microcomposite is the so-called composite in which the micro-sized particles, whiskers, platelets and fibers are dispersed at the grain boundaries of matrix grains. The nanocomposites, on the other hand, have three types of structures: intra and intergranular nanocomposites and nano/nano composite. The intra and intergranular nanocomposites were found to show the tremendous improvement of mechanical properties even at elevated temperatures compared with those of monolithic and microcomposite ceramics. The nano/nano composites gave the new functions such as machinability and superplasticity like metals. Our final goal for developing supertough and strong ceramics was achieved by hybridizing the intra and intergranular nanocomposites with the micro-meter sized fibers. This new concept was found to be also applicable for ceramic-metal composite systems.

Journal ArticleDOI
TL;DR: In this article, a new class of structural ceramic materials, called silicon carbonitride monoliths, derived from polymer powder compacts via polymer pyrolysis, are presented.
Abstract: Silicon carbonitride monoliths derived from polymer powder compacts via polymer pyrolysis represent a new class of structural ceramic materials due to the complete coalescence of the powder particles during polymer decomposition and the formation of a uniform ceramic matrix free from any grain boundaries or secondary phases. The submicron pore channel system penetrating the material can be minimized in volume by infiltration of liquid polysilazane solution or by post-HIPing so that relative densities of 96% can be reached. The monoliths are oxidation resistant up to 1600°C in air due to the formation of a highly pure silica oxidation layer and they exhibit a creep rate of 1.10 -6 s -1 at 1650°C and 90 MPa load. Initially x-ray amorphous silicon carbonitride can be crystallized in nitrogen or in air to form Si 3 N 4 /SiC or Si 3 N 4 /SiC/C nanocomposites

Journal ArticleDOI
TL;DR: In this paper, a carbon/oxide nanocomposites were formed by thermal treatment of montmorillonite/ammonium complexes, in the range 500-1000 °C.
Abstract: Carbon/oxide nanocomposites were formed by thermal treatment of montmorillonite/ammonium complexes, in the range 500–1000 °C. Although montmorillonite is decomposed above 700 °C, the lamellar structure is maintained up to 1000 °C by the presence of “intercalated” carbon. The amount of carbon in the composites can be adjusted by varying the nature of the organic ammonium cations so as to reach the computed value given by the theoretical equation for the formation of β′-SiAlON (19%). Starting from the montmorillonite/safraninium complex, the carbon content in the nanocomposite was 17.3%. β′-SiAlON was synthesized by heat treatment of this composite to 1350 °C under nitrogen. Since the oxide and the carbon source are intimately mixed on the nanoscale, β′-SiAlON is even obtained at temperatures as low as 1100 °C. Compared with other processes, the temperature for β′-SiAlON formation can be lower by approximately 300 °C.

Journal ArticleDOI
TL;DR: In this paper, a new method for synthesizing a composite made up of a spinel ferrite and an iron-cobalt alloy based on a disproportionation reaction is described.
Abstract: A new method for synthesizing a composite made up of a spinel ferrite and an iron-cobalt alloy based on a disproportionation reaction is described. In addition to a spinel phase, two metallic phases were encountered, one isomorphous to α-Fe (b.c.c. structure), the other isomorphous to cubic cobalt (f.c.c. structure). The chemical formula was determined by chemical analysis and X-ray measurements. It can be schematized by Fe 0.17 Co 0.65 [Fe 2.43 Co 0.57 O 4 ]. No oxidation of the composite is observed up to 300 °C, showing that the iron-cobalt alloy and spinel phase are surrounded and protected against oxidation. The small grain sizes, 0.1-0.5 μm, are in agreement with nanocomposite characteristics, giving outstanding magnetic properties: the saturation magnetization and coercive field are high, 90 emu g −1 and 2300 Oe respectively.

Journal ArticleDOI
TL;DR: In this paper, the powder mixtures were milled in vibrational ball mill under N2 atmosphere, and the milled powders were dynamically compacted by using a propellant gun.
Abstract: Fe100-xTix (X= 25, 50, 75 at.%) powder mixtures were milled in vibrational ball mill under N2 atmosphere, and the milled powders were dynamically compacted by using a propellant gun. It was found that Fe-Ti milled powders were consisted of α-iron and TiN phases. These powders had nanostructures with grain sizes of about 4-7 nm in diameter. By dynamically compacting the Fe50(TiN)50 powder at the shock pressures of 38.6 GPa and above, a nanocomposite material having an extremely high hardness (Hv-1300) was obtained. When the material was annealed at 1073 K for 5 h, the grain growth occurred to about 20 nm for α-iron phase, and the hardness was increased to a maximum value (Hv-1600). With increasing annealing temperature above 1173 K, the grain growth occurred and the hardness drastically decreased.

Journal ArticleDOI
TL;DR: In this paper, the authors explore the possibility of making copolymers from methlsilsesquioxane, -(MeS(O)1.5)(x-), (SiO), a precursor to black glass and polysilazane.
Abstract: : Preceramic block or graft copolymers may offer entree into nanocomposite ceramics provided the two homopolymers are immiscible and one can carefully control the size of the blocks or grafts. We are exploring the possibility of making copolymers from methlsilsesquioxane, -(MeS(O)1.5)(x-), (SiO), a precursor to black glass and the polysilazane, -(MeHSiNH)(x-), (SiMe), (SiMe), a precursor to silicon carbide nitride. Our initial efforts have been directed towards delineating the chemical transformations that SiO, prepared by room temperature catalytic redistribution of -(MeHSiO)(x-) using Cp2 TiMe2 as the catalyst (0.1 wt%), undergoes as it is heated to 900 C in N2. We find that although Cp2TiMe2 will not catalyze the redistribution of SiMe at room temperature; in the presence of even small amounts of -(MeHSiO) (x-), it is an active catalyst precursor and copolymer be formed. Spectral and chemical composition studies on the pyrolysis products of the copolymers and SiO are described.